Glass Fiber Reinforced Polymer Profiles Research Articles

Bond behaviour of smooth surface GFRP pultruded profiles with cement grout

The advantages of glass fibre reinforced polymer (GFRP) pultruded composite profiles, such as their high strength-to-weight ratio, corrosion resistance, and low maintenance costs, have attracted the attention of researchers and end users in structural applications. In spite of this, one of the challenges associated with using GFRP pultruded profiles is their smooth surfaces when bonded with concrete. To address this challenge, this study investigated four different approaches that can be used to improve the bond performance between GFRP pultruded profiles and concrete surfaces. These approaches are the incorporation of glass sand into cement grout, the variation in the size of the sand particles in the grout, the surface preparation of GFRP profiles, and the use of various cement characteristics. The experimental results show that the surface preparation of the GFRP profiles is the most effective method of improving the bond strength between the GFRP profiles and the concrete surface. Additionally, a theoretical model is developed to predict the bond behaviour, and it is observed that the linear elastic theory with the inclusion of the bond surface roughness coefficient is capable of predicting bond behaviour. The overall outcome of the study will assist design engineers and end users in the application of smooth surface GFRP profiles in concrete structures.

Formation of non-uniform fibre distribution and its effect on the flexural performance of pultruded GFRP box beams

This study investigates the effect of non-uniform fibre distribution (NUFD) as a defect in the pull-winding manufacturing process on the mechanical properties of pultruded glass fibre-reinforced polymer (GFRP) box section profiles. These profiles exhibit balanced mechanical properties but are susceptible to NUFD during production, negatively affecting local buckling capacity. Experimental and numerical analyses were conducted on pultruded GFRP profiles manufactured under three winding tension configurations, resulting in a 5% variance in load capacity during bending. Results show that corner NUFD influences local buckling capacity more than flange NUFD. Specifically, corner NUFD decreases load capacity by up to 20%, while flange NUFD increases it by up to 3%. Conversely, the effect of NUFD location is insignificant to the failure determined by the material strength without buckling instability. Moreover, a linear relationship between the rotational restraint coefficient and corner fibre volume fraction provides insight into the impact of material imperfections on load capacity.

The effects of glass fiber sheet lamination on the connection strength of single-bolted pultruded glass fiber reinforced polymer profiles

In this study, a series of experiments and finite element analyses were conducted to investigate the effects of glass fiber sheet (GFS) lamination on the strength of pin-bearing single-bolted pultruded glass-fiber-reinforced polymer (PGFRP) connections. In the experiments, nine types of GFS lamination were molded using the vacuum-assisted resin transfer molding method (VaRTM) and bonded onto the surfaces of PGFRP members. Then, four different end distances of PGFRP plates to bolt diameters ( e/ d) were surveyed, ranging from 3 to 6. The results indicated that all types of GFS lamination offered excellent improvement effects for the ultimate loads of the PGFRP connections. The strengthening effects were better when the connections had smaller e/ d values. In addition, external 0°/90° GFSs provided the best performance for GFS-strengthened PGFRP connections with medium e/ d values. Finally, it was demonstrated that finite element analysis (FEA) could be a useful method for predicting the failure loads of GFS-strengthened PGFRP connections.

Effect of Different Environmental Conditions on Durabilities of Polyester- and Vinylester-Based Glass-Fiber-Reinforced Polymer Pultruded Profiles

This paper presents the results of experimental investigations on the durability of glass-fiber-reinforced polymer (GFRP) pultruded profiles made of unsaturated polyester (UP) and vinylester (VE) resins commonly used in civil engineering. The water absorption, tensile properties, and microstructures of GFRP profiles exposed to several typical accelerated aging environments (e.g., deionized water, salt water, salt fog, and combined hygrothermal cycles) for 12 months were investigated. Moreover, a sustained loading factor was included in the test to reflect the behavior of the GFRP profiles in real structures. A normalization approach based on the controlled specimens was used to assess the effectiveness and relevance of the accelerated exposure. The results indicated that the maximum moisture absorption of both UP and VE GFRP profiles was immersed in deionized water, where the masses increased by 1.03 and 0.53%, respectively, leading to the maximum degradation of tensile strength (24.03%) of UP GFRP profile immersion in deionized water after 360 days of aging. However, the tensile modulus was more sensitive to high temperatures and has the maximum degradation (47.03%) after hygrothermal cycles. Moreover, VE GFRP profiles show superior humidity and temperature endurance. Furthermore, the sustained loading exacerbated the degradation of tensile properties slightly under the same conditions. Finally, by incorporating the cumulative damage caused by the sustained loading and a time-dependent factor into a residual strength model, a revised model was proposed to describe the tensile strength loss of pultruded UP GFRP profiles.

Non-uniform fiber-resin distributions of pultruded GFRP profiles

Pultruded fiber reinforced polymer (FRP) composite profiles are usually regarded as the transverse-isotropic material based on the assumption that the fiber and resin are uniformly distributed across the profile sections. However, this is practically not the case due to the limitations of the pultrusion technology. The non-uniform fiber-resin distribution (NUFRD), as a type of inherent initial imperfection for pultruded glass fiber reinforced polymer (GFRP) profiles, was investigated. The resin contents of 49 different pultruded GFRP sections were tested and analyzed. The standard calcination method was used to measure the resin content. The sections were provided by three different manufactures and included the I-sections, box-sections, angle-sections, circular tubes, channel-sections and flat plates. Multiple sampling locations were specified for each type of section. The test results showed that the degree of NUFRD for each type of section is different. In particular, the I-sections showed the most significant material non-uniformity. The largest COV (coefficient of variation) of the measured resin contents is 0.16. Additionally, the influence of NUFRD on the mechanical properties of GFRP members was addressed. The material non-uniformity would increase the initial section eccentricity. Finite element models were built to simulate the compressive GFRP members. It was found that the critical buckling loads of GFRP compressive members will be reduced due to NUFRD.

Fracture toughness-based models for web-crippling of pultruded GFRP profiles

This paper presents a numerical study on the web-crippling failure of pultruded glass fibre reinforced polymer (GFRP) profiles, under external-two-flange (ETF) and internal-two-flange (ITF) configurations. The numerical study is validated through experimental tests recently conducted by the authors on four I-section profiles and one U-section profile, obtained from four different suppliers. These web-crippling tests were simulated through shell finite element (FE) models where the transverse compressive fracture toughness of each GFRP material was implemented as a damage evolution parameter. In order to quantify the influence of material damage and instability effects on the web-crippling failure, three different analyses were implemented, accounting for (i) material damage, (ii) instability, and (iii) both effects. The results obtained through the analysis accounting for both material damage and instability effects showed a good agreement with experimental results, in terms of stiffness, failure modes and ultimate loads; moreover, the transverse compressive strain distributions obtained from the numerical models also agreed well with experimental results. Finally, the transverse compressive stresses were found to influence web-crippling the most, regarding both damage initiation and ultimate load stages.

Strategies to Facilitate Photovoltaic Applications in Road Structures for Energy Harvesting

Photovoltaic (PV) facilities are sustainable and promising approaches for energy harvesting, but their applications usually require adequate spaces. Road structures account for a considerable proportion of urban and suburban areas and may be feasible for incorporation with photovoltaic facilities, and thereby have attracted research interests. One solution for such applications is to take advantage of the spare ground in road facilities without traffic load, where the solar panels are mounted as their conventional applications. Such practices have been applied in medians and slopes of roads and open spaces in interchanges. Applications in accessory buildings and facilities including noise/wind barriers, parking lots, and lightings have also been reported. More efforts in existing researches have been paid to PV applications in load-bearing pavement structures, possibly because the pavement structures cover the major area of road structures. Current strategies are encapsulating PV cells by transparent coverings to different substrates to prefabricate modular PV panels in factories for onsite installation. Test road sections with such modular solar panels have been reported, where inferior cost-effectiveness and difficulties in maintenance have been evidenced, suggesting more challenges exist than expected. In order to enhance the power output of the integrated PV facilities, experiences from building-integrated PVs may be helpful, including a selection of proper PV technologies, an optimized inclination of PV panels, and mitigating the operational temperature of PV cells. Novel integrations of amorphous silicon PV cells and glass fiber reinforced polymer profiles are proposed in this research for multi-scenario applications, and their mechanical robustness was evaluated by bending experiments.

Monotonic and cyclic behaviour of cuff beam-to-column connection system for tubular pultruded GFRP profiles

The use of glass-fibre reinforced polymer (GFRP) cuff parts to join GFRP beams and columns has been object of several experimental and numerical studies in the past, which showed their improved mechanical performance when compared to connection systems that mimic steel structures, such as connections with GFRP web and/or flange cleats. The main objective of the study presented in this paper is to propose and assess a connection system – for tubular GFRP profiles –with similar cuff geometry, but made of stainless steel, in order to achieve higher ductility due to its inherent strain hardening, while maintaining the non-corrodibility capabilities of GFRP. Full-scale tests were performed on four different beam-to-column connection series using stainless steel cuffs with varying geometry and plate thickness. The experimental campaign comprised: (i)monotonic tests for all series; and (ii)cyclic tests for the series with the best performance in the monotonic tests. The monotonic response of the different series varied considerably. As expected, by increasing the plate thickness of the cuff, the initial stiffness and strength of the connections were substantially improved; on the other hand, the moment vs. rotation behaviour of connections with thinner cuff parts was more markedly non-linear and GFRP damage was delayed. Nevertheless, all connection series presented significant ductility, successfully making use of the stainless steel mechanical properties. For both monotonic and cyclic loading, the cuff connection system presented herein provided better mechanical performance than stainless steel sleeve connections developed earlier by the authors, namely regarding initial stiffness, overall strength and energy dissipation.

An Efficient Approach to Describe the Fiber Effect on Mechanical Performance of Pultruded GFRP Profiles

This study focuses on the flexural behavior of pultruded glass fiber-reinforced polymer (GFRP) profiles developed for structural applications. Fiber content is a commonly accepted measure for estimating the resistance of such components, and technical datasheets describe this essential parameter. However, its direct implementation to the numerical simulations can face substantial problems because of the limitations of standard test protocols. Furthermore, the fiber mass percentage understandable for producers is unsuitable for typical software considered the volumetric reinforcement content. This manuscript exemplifies the above situation both experimentally and analytically, investigating two GFRP square hollow section (SHS) profiles available at the market. A three-point bending test determines the mechanical performance of the profiles in this experimental program; a digital image correlation system captures deformations and failure mechanisms of the SHS specimens; a standard tensile test defines the material properties. A simplified finite element (FE) model is developed based on the smeared reinforcement concept to predict the stiffness and load-bearing capacity of the profiles. An efficient balance between the prediction accuracy and computation time characterizes the developed FE approach that does not require specific descriptions of reinforcement geometry and refined meshes necessary for modeling the discrete fibers. The proposed FE approach is also used to analyze the fiber efficiency in reinforcing the polymer matrix. The efficiency is understood as the model’s ability to resist mechanical load proportional to the dry filaments’ content and experimental elastic modulus value. Scanning electron microscopy relates the composite microstructure and the mechanical performance of the selected profiles in this study.

Exterior beam-to-column bolted connections between GFRP I-shaped pultruded profiles using stainless steel cleats. Part 1: Experimental study

Beam-to-column connections are very relevant in the design of glass fibre reinforced polymer (GFRP) structures, since they can (i) govern the load capacity and robustness, presenting brittle failure modes, and (ii) reduce the deflections of GFRP flexural members. This paper presents a study about the mechanical behaviour of exterior beam-to-column connections between I-shaped pultruded GFRP profiles using stainless steel cleats. The main objective was to develop a connection system with non-corrodible auxiliary parts and improved ductility, by exploiting the stainless steel properties. For that, full-scale tests were performed to investigate (i) the monotonic response of nine different connection series, and (ii) the cyclic response of four of those series. The series differed in the number of bolts/rods (one or two bolt rows), cleat thickness (3, 6 and 8 mm), position of the cleats (flange or web) and use of column reinforcements, materialized by stainless steel rods and plates connecting the cleats to the columns’ back flange. All series that did not include such reinforcements presented tensile rupture at the columns’ web-flange junction at a very initial stage of the monotonic and cyclic tests, limiting the connections’ strength, ductility and capacity to dissipate energy. In the reinforced series, where this failure mode was avoided, the stiffness, strength, ductility and energy dissipation was highly influenced by the cleats thickness and bolts row number. The series that presented the best overall mechanical behaviour comprised 6 mm thick flange cleats, each with two bolt rows, and column reinforcements; in this series, the intermediate thickness of the cleats provided the best balance between the initial stiffness and non-linear deformation capacity, delaying GFRP local failure and allowing to mobilize the stainless steel ductility — this connection presented the highest strength and energy dissipation capacity. In addition to the experimental study presented herein, Part 2 (Martins et al., 2021) presents predictions of the stiffness and strength of the reinforced connection series using analytical and numerical methods.

Effect of fibre layup and bearing length on the web-crippling behaviour of pultruded GFRP profiles

This paper presents an experimental study about the web-crippling behaviour of pultruded glass fibre reinforced polymer (GFRP) profiles, loaded under end two flange (ETF) and interior two flange (ITF) configurations, with varying bearing lengths. The study was performed to address two significant research needs: (i) to obtain a better understanding of the web-crippling phenomenon in GFRP profiles with different cross-sections and fibre layups; and (ii) to provide additional experimental data on web-crippling, necessary to validate advanced numerical models and to develop design formulae. The experimental programme included materials with different levels of transverse reinforcement, provided by a total of four suppliers. These significant differences in the fibre layups among the profiles tested did not seem to affect the stiffness and ultimate loads significantly. To the contrary, the bearing length was found to have a significant effect on the failure mode, stiffness and ultimate load of all I-section profiles. Moreover, and despite their significant differences in terms of geometrical and material properties, all I-section profiles presented similar transverse compressive strain distributions, when loaded in the same conditions, showing that changes in fibre layups had a negligible effect on the effective bearing length of the various specimens.

Effect of Web Stiffeners on The Flexural Behavior of Composite GFRP- Concrete ‎Beam Under Impact Load

In this paper, numerical and experimental studies on the elastic behavior of glass fiber reinforced ‎polymer (GFRP) with stiffeners in the GFRP section's web (to prevent local buckling) are presented. ‎The GFRP profiles‎ were connected to the concrete deck slab by shear connectors. Two full-scale simply supported ‎composite beams (with and without stiffeners) were tested under impact load (three-point load) to ‎assess its structural response. The results ‎proved that the maximum impact force, maximum ‎deflection, damping time, and ‎damping ratio of the composite beam were affected by the GFRP ‎stiffeners‎. The experimental results indicated that the damping ratio and deflection were diminished compared to hybrid beam without stiffeners by ‎‎16% and 22%, respectively, and increasing damping time‏ by 26%. Finite element models were used to study pre-failure behavior. ‎ The numerical modeling results showed good agreement with experimental data in terms of loading path and ‎final load. The damping ratio and midspan deflection values were greater than the experimental ‎values by 6% and 12%, respectively.

Mechanical properties of pultruded GFRP profiles under seawater sea sand concrete environment coupled with UV radiation and moisture

In this research, the mechanical properties of various glass fibre reinforced polymer (GFRP) pultruded profiles exposed to seawater sea sand concrete (SWSSC) and its combination with UV radiation and water vapour condensation were studied. The effect of different conditions, duration of conditioning, and the profile cross-section configuration on the mechanical properties were investigated. Three-point bending, tension, and compression tests were carried out to obtain the mechanical properties, including flexural, tensile and compressive strengths and tensile elastic modulus. Furthermore, in order to scrutiny the mechanisms and extent of damage, scanning electron microscopy (SEM) was carried out on the test samples before and after the exposures. Finally, regression models were derived according to the experimental data to describe the mechanical properties of profiles after exposure to the aggressive environments used in this study. The maximum reductions of about 30%, 33% and 46% were observed in three-point bending, tensile and compressive tests, respectively amongst all samples when exposed for 90 days to simulated SWSSC. These reductions increased for the same sections to 52%, 47%, and 50% when the GFRP profiles were pre-exposed for 3000 h to UV radiation and moisture before exposing for 90 days to simulated SWSSC.

The effect of elevated temperatures on the compressive section capacity of pultruded GFRP profiles

The compressive performance of glass fiber reinforced polymer (GFRP) profiles subjected to elevated temperature was investigated through a large number of (3 0 0) tests. The effects of profile cross-sectional area, slenderness, and temperature on the behavior of the GFRP profiles at temperatures ranging from 25 to 400 °C were determined. It was observed that the compressive strength of the GFRP profiles has been decreased by half as the temperature exceeded 90 °C, i.e., close to the glass transition temperature of the matrix. The temperature and ratio of cross-sectional area to external perimeter were determined as two major parameters affecting section capacity.

Flexural behavior of timber beams strengthened with pultruded glass fiber reinforced polymer profiles

Timber is one of the materials widely used in construction and industry all over the world. In this paper, the behavior of strengthened timber beams made of beech wood (Fagus orientalis) were investigated experimentally. The composite timber beams were reinforced with flat, U-shaped, and L-shaped pultruded Glass Fiber Reinforced Polymer (GFRP) profiles. The GFRPs were attached to tensile or both tensile and compressive surfaces of beams. Altogether, 24 specimens, including 20 strengthened beams and 4 un-strengthened (control) beams, were tested under three-point bending test. Flexural behavior of specimens was evaluated through their load versus mid-span displacement curves, ultimate load carrying capacity, stiffness, displacement ductility, and capacity of energy absorption. The experimental results indicated that the mean value of modulus of rupture, flexural rigidity, ductility, and energy absorption of strengthened beams increased by up to 61, 59, 79, and 209% in comparison to control specimens, respectively. Finally, an analytical calculation has been conducted in order to predict the test data. There was a reasonable agreement between the test results and the results of numerical model.

Effect of thermal cycles on mechanical response of pultruded glass fiber reinforced polymer profiles of different geometries

This study investigates the effect of Thermal cycles on the mechanical properties of GFRP pultruded profiles with different geometries. Bending specimens consisted of I-shaped and U-channel profiles that were tested in three-point bending along their both principal weak and strong axes, whereas box profiles and laminates were used in compression and tension tests, respectively. Each specimen was exposed to a range of thermal cycles, between −20 °C and 20 °C. The failure modes of the profiles were closely investigated at both major and minor scales. Results were analyzed using ANOVA to determine the influence of each factor and a model was developed to predict the strength retention of profiles after exposure to thermal cycles. The results showed that the thermal cycles have a significant effect on the strength of the resin and a minor effect on the strength of the fibers. Bending specimens experienced a lower strength loss along their principal weak axis than that along their strong axis after conditioning. Tension specimens performed better in comparison to compression specimens in terms of strength retention after thermal exposure. These results are expected to contribute significantly toward the understanding of the influence of thermal cycles on the behavior of GFRP profiles.

High-cycle fatigue constitutive model and a load-advance strategy for the analysis of unidirectional fiber reinforced composites subjected to longitudinal loads

A fatigue constitutive model valid for the composite constituent will be presented in this paper. The composite behaviour will be obtained by means of the serial/parallel mixing theory that is also used as a constitutive equation manager. The constitutive formulation is coupled with a load advancing strategy in order to reduce the computational cost of the numerical simulations. Validation of the constitutive formulation is done on pultruded glass fiber reinforced polymer profiles. Special emphasis is made on the comparison between the experimental and the numerical failure mode.

Two-dimensional Modelling of Thermal Responses of GFRP Profiles Exposed to ISO-834 Fire

In the past three decades, one-dimensional (1-D) thermal model was usually used to estimate the thermal responses of glass fiber-reinforced polymer (GFRP) materials and structures. However, the temperature gradient and mechanical degradation of whole cross sections cannot be accurately evaluated. To address this issue, a two-dimensional (2-D) thermo-mechanical model was developed predict the thermal and mechanical responses of rectangular GFRP tubes subjected to one-side ISO-834 fire exposure in this paper. The 2-D governing heat transfer equations with thermal boundary conditions, discretized by alternating direction implicit (ADI) method, were solved by Gauss-Seidel iterative approach. Then the temperature-dependent mechanical responses were obtained by considering the elastic modulus degradation from glass transition and decomposition of resin. The temperatures of available experimental results can be reasonably predicted. This model can also be extended to simulate the thermo-mechanical responses of beams and columns subjected to multi-side fire loading, which may occur in real fire scenarios.

Influence of glued-in reinforcement profiles on the thermal characteristics of wooden window profiles

Nowadays wooden windows represent high aesthetic value to modern buildings. There is a strong trend of increasing their dimensions, especially their height, which causes problems considering their stability and load bearing capacity. Aluminium, stainless steel, carbon-fiber reinforced polymer profiles and glass-fiber reinforced polymer profiles, with different geometry and orientation, were used to reinforce wooden window mullion. Since reinforcing materials have usually higher thermal conductivity as wood, their effect on the thermal performance of the window as a whole, was examined in this study. Thermal transmittance of several different reinforced profiles was analyzed to select an optimal solution. It was concluded that reinforcing material does not have significant effect on thermal transmittance of window frame, if reinforcement is not placed through the entire thickness of the window profile. If this is the case, only glass-fiber reinforced polymer, with a maximum of 22 % reinforcing material in window profile, fulfils the standard criteria for low energy buildings. The effect of type and geometry of reinforcing materials have minor effect on thermal transmittance of entire window, but have great impact on the minimal local inside surface temperatures, which can lead to condensation and mould growth.

Creep behaviour of plane frame structures made of GFRP profiles

A methodology is presented for analytical calculation of creep behavior of plane frames made of glass fiber reinforced polymer (GFRP) profiles and an experimental study is carried out in order to evaluate the analytical calculation results. In order to account nonlinear viscoelastic material behavior, stress – strain – time relationship of plane frame is given and creep behavior of plane frame structure is investigated. Material coefficients for the creep functions are determined using three point beam bending test results. In order to validate the analytical approach, a plane frame made of GFRP profiles is tested under sustained loads for 100 days and displacements, strains are monitored. Strain and displacement values that are calculated using analytical method show good agreement with the full-scale test data. DOI: http://dx.doi.org/10.5755/j01.mech.23.3.14029